Thirty species and subspecies of rattlesnakes occur in the United States, more than half of this number being found in the Southwest. Because they have been killed on sight for years, their numbers have been considerably reduced in densely populated areas. For this reason, together with emphasis placed upon their poisonous characteristics by some writers of western thriller fiction, rattlesnakes are considered by many people to be a serious menace in the thinly populated portions of the arid West[8]. [Illustration: _Western diamondback rattlesnake_ (_Crotalus atrox._) (Photo by Earl Jackson)] _Where rattlesnakes are found_ In the hot desert regions of the Southwest rattlesnakes are usually abroad at night during the summer months, as they have no controlling system for body temperature and cannot endure the heat at ground surface during the hours of sunlight. In spring and autumn they may be encountered in the daytime but during December, January, and February they are in hibernation and are rarely or never seen. Their food consists principally of lizards and small rodents such as ground squirrels, rats, mice, pocket gophers and young rabbits. They are sometimes found along irrigation canal banks where they go for water, and because they find rodents congregating there for the same reason. Unless surprised, cornered, teased, handled, or injured, a rattlesnake usually will try to remain hidden or will endeavor to crawl away rather than strike. Because they are attracted to places where small rodents abound, they are sometimes encountered around barns and outbuildings. They occasionally enter abandoned structures in search of food or to escape from the heat of the sun. _Protective clothing_ Because a rattlesnake may be met at almost any time, except during the winter months, by a person who lives, works, or visits in the desert, he should be ever alert. If hiking or climbing through country where rattlesnakes are known to be abundant, he should wear clothing that will protect him from a possible bite. Pope[9] states that records kept during 1928 and 1929 show that 98 per cent of snake bites occurred below the knee or on the hand or forearm. When in snake country, the hiker should wear knee-high boots or leggings, and should never place his hand on a rock or ledge above the level of his eyes. In other words, watch your step, and look before you reach! Apparently rattlesnakes may strike at a quick movement and are very sensitive to the body warmth of a nearby warm-blooded creature. _Rattlesnake relatives_